1. Field of the Invention
The present invention relates to a preparation process of a phthalide compound useful as a color former of color-developing recording materials.
2. Related Art of the Invention
A 3,3-bisarylphthalide compound having amino groups, 3,3-bis(4-dimethylaminophenyl) -6-dimethylaminophthalide(crystal violet lactone) in particular, is widely used for pressure sensitive copying papers and thermal recording papers as a color former which develops blue color.
Japanese Laid-Open Patent SHO 62-184061, SHO 55-120562 and HEI 02-47160 have described processes for preparing a phthalide compound by oxidizing a triarylmethene compound. However, these preparation processes have led to problems. For example, the reaction system increases alkali concentration with the progress of the reaction in these preparation processes and causes problems of permanently remaining unreacted raw materials. Further, a metal compound is added in order to accelerate the reaction and remains in the waste water in the step of filtering and washing the phthalide reaction product. Such residual materials have caused problems of increasing the cost of waste water disposal.